[PATCH] Enhancement proposal for usage of Method::getParameterTypes

[Claes Redestad]

Hi,

some or all of these were pointed out as part of
https://bugs.openjdk.java.net/browse/JDK-8029019

There was a patch out for review early 2017. I'm not sure what happened
to that?

Either way I think it might make sense to get this small and trivial
enhancement separated out and fixed.

Thanks!

/Claes

On 2019-11-08 23:04, Сергей Цыпанов wrote:
> Hello,
> 
> it seems like Method.getParameterTypes() is often misused in JDK (and beyond): array returned from the method is used only to acquire number of method params by retrieving array.length.
> The problem here is that Method.getPatameterTypes() clones underlying array and returns the copy.
> Instead we can use Method.getParameterCount() which doesn't allocate any additional memory but returns directly the length of underlying  array.
> 
> To measure probable performance difference I've created a benchmark for the most simple case when tested method has no parameters:
> 
> @State(Scope.Thread)
> @BenchmarkMode(Mode.AverageTime)
> @OutputTimeUnit(TimeUnit.NANOSECONDS)
> public class MethodToStringBenchmark {
>    private Method method;
> 
>    @Setup
>    public void setup() throws Exception { method = getClass().getMethod("toString"); }
> 
>    @Benchmark
>    public int getParameterCount() { return method.getParameterCount(); }
> 
>    @Benchmark
>    public int getParameterTypes() { return method.getParameterTypes().length; }
> }
> 
> on my i7-7700 with JDK 11 it produces these results:
> 
> 
> Benchmark                                                               Mode  Cnt     Score    Error   Units
> 
> MethodToStringBenchmark.getParameterCount                               avgt   25     2,528 ±  0,085   ns/op
> MethodToStringBenchmark.getParameterCount:·gc.alloc.rate                avgt   25    ≈ 10⁻⁴           MB/sec
> MethodToStringBenchmark.getParameterCount:·gc.alloc.rate.norm           avgt   25    ≈ 10⁻⁷             B/op
> MethodToStringBenchmark.getParameterCount:·gc.count                     avgt   25       ≈ 0           counts
> 
> MethodToStringBenchmark.getParameterTypes                               avgt   25     7,299 ±  0,410   ns/op
> MethodToStringBenchmark.getParameterTypes:·gc.alloc.rate                avgt   25  1999,454 ± 89,929  MB/sec
> MethodToStringBenchmark.getParameterTypes:·gc.alloc.rate.norm           avgt   25    16,000 ±  0,001    B/op
> MethodToStringBenchmark.getParameterTypes:·gc.churn.G1_Eden_Space       avgt   25  2003,360 ± 91,537  MB/sec
> MethodToStringBenchmark.getParameterTypes:·gc.churn.G1_Eden_Space.norm  avgt   25    16,030 ±  0,045    B/op
> MethodToStringBenchmark.getParameterTypes:·gc.churn.G1_Old_Gen          avgt   25     0,004 ±  0,001  MB/sec
> MethodToStringBenchmark.getParameterTypes:·gc.churn.G1_Old_Gen.norm     avgt   25    ≈ 10⁻⁵             B/op
> MethodToStringBenchmark.getParameterTypes:·gc.count                     avgt   25  2380,000           counts
> MethodToStringBenchmark.getParameterTypes:·gc.time                      avgt   25  1325,000               ms
> 
> I've prepared a small patch to replace usage of getParameterTypes() with getParameterCount() where appropriate in java.base module.
> 
> The patch is attached.
> 
> Regards,
> Sergey Tsypanov
>